Abstract. During the ESCOMPTE precampaign (summer 2000, over Southern France), a 3-day
period of intensive observation (IOP0), associated with ozone peaks, has been
simulated. The comprehensive RAMS model, version 4.3, coupled on-line with a
chemical module including 29 species, is used to follow the chemistry of the
polluted zone. This efficient but time consuming method can be used because
the code is installed on a parallel computer, the SGI 3800. Two runs are
performed: run 1 with a single grid and run 2 with two nested grids. The
simulated fields of ozone, carbon monoxide, nitrogen oxides and sulfur dioxide
are compared with aircraft and surface station measurements. The 2-grid run
looks substantially better than the run with one grid because the former takes
the outer pollutants into account. This on-line method helps to satisfactorily
retrieve the chemical species redistribution and to explain the impact of
dynamics on this redistribution.